High-speed tool steel



Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE Firth, Pittsburgh, Pa.,

assignors to Firth- Sterling Steel Company, a corporation of Pennsylvania No Drawing.

4 Claims.

This invention relates to high-speed tool steel of molybdenum type. Molybdenum as an alloying element in high-speed tool steels is used as an equivalent or as a partial replacing element for tungsten. See Gregg, The Alloys of Iron and Molybdenum, publishedfor The Engineering Foundation, New York and London, 1932, page 315. On page 316 the author adds, That molybdenum can be considered a substitute for tungsten has been known for over thirty years. It has, however, been found that, in the heat treatment of tools made from molybdenum steel, a tendency to softening of the-metal at or near the surface appears (Gregg, pp. 323, 325, 345, 346, 356); and it has been the practice, as a review of the compositions given by Gregg will show, to include with molybdenum in the mix a substantial chromium content.

We have discovered that boron may advantageously be included in the mix; that, if boron be present in quantity and under circumstances presently tobe specified, the presence of chromium is not requisite. It may be eliminated entirely and in no case should it be present in an amount exceeding 1.50%. A molybdenum highspeed steel is thus produced which is free of any tendency to deterioration during heat treatment, and which possesses'the desirable qualities that characterize the type. Indeed, the steel of our invention has showed itself to be notably supe- 30 rior, in the matter of toollife, to typical molybdenum steels of common acceptance in the indus try. We have by investigation determined the circumstances and the limitations under which boron may be employed with advantage.

In the following Table I the compositions are given of the non-ferrous portions of steels that we have found to be of the desired high quality.

V Cu Ni Low Application January 21, 1939, Serial No. 252,214

regarded as typical have determined values of 4.02; 5.60; 8.02; and 9.50, respectively, while our steel I revealed a tool life of 18.50.

Of these nine steels it will be noted that four components are persistent throughout-carbon, vanadium, molybdenum, and boron. Two (III and IVIII being most excellent) contain these four components and no others. 'The carbon content in no case exceeds 1%, and the boron content in every case is definitely less in value m than the carbon; in all cases .but two (II and VII) the boron content is less than half the carbon; in one of those two (VII) it is, with slight tolerance, substantially one half the carbon; and in two cases (I, 11-01? which I was most excellent) the carbon and the boron contents together are less in value than 1%. Chromium,

' present in three of the nine steels, is absent from six; its presence at most amounts to 1.07%; and its lack of significance is well indicated by the fact that, of the three most excellent steels, one (I) contains it in maximum amount, while the other two (III and VIII) contain none of it. The molybdenum content ranges from 8 to 9.36%, and the vanadium from 0.75 to 1.40%.

In the foregoing table percentages are given with relation to the iron content. Taking the essential elements of these specimen steels carbon, vanadium, molybdenum, boron, and iron and reducing all to percentages of the whole,

we have- C V Mo B Fe In Table II the compositions are given of the non-ferrous portions of six more steels of the invention.

OSiMnGrVMoCoBCuNi These all were found to be steels of desired quality. The carbon content ranges from 0.65 to 1%; the boron content ranges from 6 to $4, of

the carbon content; and in only one case (m) do the combined carbon and boron contents exceed 1%. Chromium is, in three cases (XII.

m, and XV) entirely absent; and, at most (XI) is present in the amount of 0.89%. Molybdenum ranges from 7.85 to 8.25%, and vanadium from 0.78 to 2.36%.

Reducing the values of the essential elements 10 of Table II to percentages of the whole, we have C V M B Fe i 20 In Table III the compositions are given of the non-ferrous portions of five more steels of the invention.

Si Mn Cr V Mo 00 B Cu Ni 0 V Mo 13 Fe 1.33 7.58 0.65 90.17=1oo 1.25 8.59 421 s9.29=9999 2.02 7.42 ..73 saea=1o0o1 1.08 7.78 0.53 9o.2a=10o 0.89 7.25 0.4 91.14=1oo Taking the three tabulations together, it appears that, although chromium may be present, it may be entirely absent; and that, when present, its magnitude does not exceed 1.07%. Our experimentation has indicated to usythat the upper lmrit for chromium is 1.50% of the iron content. Cobalt when present ranges from 2.33 55 to 8.90; and our experiments indicate that the upperllmit for cobalt is 10% of the iron content.

Of the four persistent elements (molybdenum.

vanadium, carbon, and boron) the molybdenum content ranges from 7.85 to 9.62%, and our experimentation has indicated to us a permissible range for molybdenum of -12% of the iron content. Associated with molybdenum is vanadium in an amount of 0.75-2.36%; and here the "limits are 0.25-2.50%. The carbon component in no case exceeds 1% of the iron content; the boron component ranges from 0.10 to 0.91%, and in no case exceeds 1% of the' iron content; and the combined carbon and boron components range from 0.78 to 1.25%, and in the majority of cases range from 0.90 to 1.10% of the iron content. ,The maximum value of the combined carbon and boron contents, in percentage relative to the whole, is 1.13%. We have dwelt upon the fact that chromium may be wholly lacking,

and that, if present, it should not exceed a value of 1.50% of the ire content. Copper may be present in small am unts. If present, the quantity according to the foregoing table does not exceed 3%, and our investigations indicate that in no case should the copper content exceed 3.50% of the iron content. As has been indicated in the foregoing tables, other elements, adventitiously present, do not disturb the essential composition of the ensuing claims.

We claim as our invention 1. A high-speed tool steel of the molybdenumtype of the following composition: carbon, 0.07-

0.90%; vanadium, 0.682.12%; molybdenum, 7.06-

8.59%; boron, 0.09-0.81%; and iron, 89.29-91.21%, the boron and carbon together not exceeding 1.13%, and free of chromium in excess of 1.50% of the iron content.

2. A high-speed tool steel of molybdenum type, of the following composition: carbon, GAE-0.90%; vanadium, 0.68-1.25%; molybdenum, 7.25-8.38%; boron, 0.20-0.38%; and iron, 89.54-90.59%, and freeof chromium in excess of 1.50% of the iron content.

3. A high-speed tool steel of molybdenum type, of the following composition: carbon, 0.59-0.90%; vanadium, 0.71-'-2.12%; molybdenum, 7.06-7.44%; boron, 0.09-0.14%; and iron, 89.95-91.21%,' and free of chromium in excess of 1.50% of the iron content.

4. A high-speed tool steel of molybdenum type, of the following composition:- carbon, 0.07-0.46%; vanadium, 0.69-2.02%; molybdenum, 7.25%- 8.59; boron, 0.46-0.81%, and iron, 89.29-91.14%, and free of chromium in excess of 1.50% of the iron content.

EIMER B. WELCH. LEWIS GERALD FIRTH. 

